package com.youxuit.youxu.utils;

public class CharsetTool {
    static int TMIN = 1;
    static int TMAX = 26;
    static int BASE = 36;
    static int INITIAL_N = 128;
    static int INITIAL_BIAS = 72;
    static int DAMP = 700;
    static int SKEW = 38;
    static char DELIMITER = '-';

    /**
     * Punycodes a unicode string.
     *
     * @param input
     *            Unicode string.
     *
     * @return Punycoded string.
     */
    public static String encode(String input) throws Exception {
        int n = INITIAL_N;
        int delta = 0;
        int bias = INITIAL_BIAS;
        StringBuilder output = new StringBuilder();
        // Copy all basic code points to the output
        int b = 0;
        for (int i = 0; i < input.length(); i++) {
            char c = input.charAt(i);
            if (isBasic(c)) {
                output.append(c);
                b++;
            }
        }
        // Append delimiter
        if (b > 0) {
            output.append(DELIMITER);
        }
        int h = b;
        while (h < input.length()) {
            int m = Integer.MAX_VALUE;
            // Find the minimum code point >= n
            for (int i = 0; i < input.length(); i++) {
                int c = input.charAt(i);
                if (c >= n && c < m) {
                    m = c;
                }
            }
            if (m - n > (Integer.MAX_VALUE - delta) / (h + 1)) {
                throw new Exception("OVERFLOW");
            }
            delta = delta + (m - n) * (h + 1);
            n = m;
            for (int j = 0; j < input.length(); j++) {
                int c = input.charAt(j);
                if (c < n) {
                    delta++;
                    if (0 == delta) {
                        throw new Exception("OVERFLOW");
                    }
                }
                if (c == n) {
                    int q = delta;
                    for (int k = BASE;; k += BASE) {
                        int t;
                        if (k <= bias) {
                            t = TMIN;
                        } else if (k >= bias + TMAX) {
                            t = TMAX;
                        } else {
                            t = k - bias;
                        }
                        if (q < t) {
                            break;
                        }
                        output.append((char) digit2codepoint(t + (q - t)
                                % (BASE - t)));
                        q = (q - t) / (BASE - t);
                    }
                    output.append((char) digit2codepoint(q));
                    bias = adapt(delta, h + 1, h == b);
                    delta = 0;
                    h++;
                }
            }
            delta++;
            n++;
        }
        return output.toString();
    }

    /**
     * Decode a punycoded string.
     *
     * @param input
     *            Punycode string
     *
     * @return Unicode string.
     */
    public static String decode(String input) throws Exception {
        int n = INITIAL_N;
        int i = 0;
        int bias = INITIAL_BIAS;
        StringBuilder output = new StringBuilder();
        int d = input.lastIndexOf(DELIMITER);
        if (d > 0) {
            for (int j = 0; j < d; j++) {
                char c = input.charAt(j);
                if (!isBasic(c)) {
                    throw new Exception("BAD_INPUT");
                }
                output.append(c);
            }
            d++;
        } else {
            d = 0;
        }
        while (d < input.length()) {
            int oldi = i;
            int w = 1;
            for (int k = BASE;; k += BASE) {
                if (d == input.length()) {
                    throw new Exception("BAD_INPUT");
                }
                int c = input.charAt(d++);
                int digit = codepoint2digit(c);
                if (digit > (Integer.MAX_VALUE - i) / w) {
                    throw new Exception("OVERFLOW");
                }
                i = i + digit * w;
                int t;
                if (k <= bias) {
                    t = TMIN;
                } else if (k >= bias + TMAX) {
                    t = TMAX;
                } else {
                    t = k - bias;
                }
                if (digit < t) {
                    break;
                }
                w = w * (BASE - t);
            }
            bias = adapt(i - oldi, output.length() + 1, oldi == 0);
            if (i / (output.length() + 1) > Integer.MAX_VALUE - n) {
                throw new Exception("OVERFLOW");
            }
            n = n + i / (output.length() + 1);
            i = i % (output.length() + 1);
            output.insert(i, (char) n);
            i++;
        }
        return output.toString();
    }

    public static int adapt(int delta, int numpoints, boolean first) {
        if (first) {
            delta = delta / DAMP;
        } else {
            delta = delta / 2;
        }
        delta = delta + (delta / numpoints);
        int k = 0;
        while (delta > ((BASE - TMIN) * TMAX) / 2) {
            delta = delta / (BASE - TMIN);
            k = k + BASE;
        }
        return k + ((BASE - TMIN + 1) * delta) / (delta + SKEW);
    }

    public static boolean isBasic(char c) {
        return c < 0x80;
    }

    public static int digit2codepoint(int d) throws Exception {
        if (d < 26) {
            // 0..25 : 'a'..'z'
            return d + 'a';
        } else if (d < 36) {
            // 26..35 : '0'..'9';
            return d - 26 + '0';
        } else {
            throw new Exception("BAD_INPUT");
        }
    }

    public static int codepoint2digit(int c) throws Exception {
        if (c - '0' < 10) {
            // '0'..'9' : 26..35
            return c - '0' + 26;
        } else if (c - 'a' < 26) {
            // 'a'..'z' : 0..25
            return c - 'a';
        } else {
            throw new Exception("BAD_INPUT");
        }
    }

    public static void main(String[] args) throws Exception {
        String strPunycode ="xn--"+ CharsetTool.encode("北京大学");
        System.out.println(strPunycode);
        String strChinese = CharsetTool.decode("1lq90ic7fzpc");
        System.out.println(strChinese);
    }
}
